1. Field of the Invention
This invention relates to a screen communications system that enables quick across to content-of-screen-display modifying information between a plurality of mutually communicable terminal units which display the same contents on the respective display screens.
2. Description of the Related Art
Heretofore the screen communications system of the above-described type is exemplified by a personal computer conference system.
In this known computer conference system, in order to guarantee that the screen displays of all terminal units are identical, a screen modifying right is moved by transferring a modifying right request command and a modifying right moving command. Since these commands are executed according to a store-and-forward protocol similar to the transfer of screen modifying data, a user needs to perform at least two steps of requesting a modifying right and modifying the content of the screen display.
With this prior art, the operation for requesting a modifying right must be performed before actually modifying the content of screen display, which is laborious and time-consuming.
To this end, a graphics conference system has been proposed, such as disclosed in Japanese Patent Laid-Open Publication No. SHO 62-269585, in which the individual terminal unit has a built-in switch so that a modifying right can be moved by receiving a signal requesting the opening of the switch and by transmitting a signal indicating the completion of the opening of the switch.
In this graphics conference system, the terminal unit whose switch is closed has a modifying right; when a screen modifying operation is performed at the terminal unit whose switch is open, the terminal unit transmits a signal requesting the opening of the switch and does not close the switch until a signal indicating the completion of the opening of the switch is returned.
Since only one of the switches will be open at any point in time, it is possible to move a modifying right in a single screen modifying operation, while guaranteeing the uniformity of screen display.
However, until a signal indicating the completion of the opening of the switch is returned after a signal requesting the opening of the switch is transmitted, the terminal unit cannot discriminate whether or not the built-in switch may be closed. As a result, the terminal unit cannot discriminate whether or not it has a modifying right by itself, and the delay time from the screen modifying operation to the reaction of the display of the terminal unit will become large, thus diminishing operation of the terminal unit. Therefore quick movement of a modifying right cannot be achieved.